The Message Passing Interface (MPI) is a standardized system for passing messages between compute nodes or processes in parallel computing systems. MPI defines point-to-point message ordering between two processes based on the matching criteria of MPI messages: a user-supplied tag, sender process (i.e., the source rank), and a communicator identifier (e.g., context ID). MPI is generally deterministic except that nondeterminism may arise when wildcards are used and messages are received from multiple senders. MPI message processing engines typically split message processing into two separate structures: a first for handling posted receive operations and a second for handling unexpected messages. In particular, if a received message does not match a previous posted receive, the message is unexpected and therefore may be stored in that data structure. The FIFO-like semantic and presence of wildcards, for example, often draw MPI implementations toward storing posted receive operations and unexpected messages in single message queues, implemented as linked lists that are ordered from oldest to newest.